future train (electricity generated from heat loss) report

FUTURE TRAIN (ELECTRICITY GENERATION FROM HEAT LOSS)

PROJECT I

SUBMITTED IN PARTIAL FUFILLMENT OF THE REQUIREMENT

FOR THE AWARD OF THE DEGREE

BACHELOR OF TECHNOLOGY(MECHANICAL ENGINEERING)

SUBMITTED BYRISHABH (2812493)

RAJ KISHOR (2812485)

RAVI PANDEY (2812489)

SHAHZAIB (2812484)

RISHI KUMAR (2812494)

RAVI KUMAR (2812235)

KURUKSHETRA UNIVERSITY, KURUKSHETRA

NOVEMBER, 2015

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FUTURE TRAIN (ELECTRICITY GENERATION FROM HEAT LOSS)

PROJECT I

SUBMITTED IN PARTIAL FUFILLMENT OF THE REQUIREMENT

FOR THE AWARD OF THE DEGREE

BACHELOR OF TECHNOLOGY

(MECHANICAL ENGINEERING)

SUBMITTED BY

RISHABH (2812493)



SHAHZAIB (2812484)



PANIPAT INSTITUTE OF ENGINEERING & TECHNOLOGY,

SAMALKHA

NOVEMBER 2015

KURUKSHETRA UNIVERSITY KURUKSHETRA1

DECLARATION

We hereby certify that the work which is being presented in the project entitled “Future train (electricity generated from heat loss)” by “Rishabh (2812493), Rajkishor (2812485), Ravi pandey (2812489), Shahzaib (2812484), Rishi (2812494), Ravi (2812235)” in partial fulfillment of requirements for the award of degree of B.Tech (Mechanical Engineering) submitted in the department of mechanical engineering at PANIPAT INSTITUTE OF ENGINEERING & TECHNOLOGY, SAMALKHA afflicated to KURUKSHETRA UNIVERSITY, KURUKSHETRA is carried out during a period from AUG 2015 to NOV 2015 under the supervision of Er. Ajay Chokker of project guide. The matter presented in the project has not been submitted by us in any other university / institute for the award of B.Tech degree.

RISHABH (2812493)



SHAHZAIB (2812484)



This is to certify that the above statement made by the candidate is correct to the best of my / our knowledge.

(Er. Ajay singh) Er. Amit Dubey

A.P. Mech Deptt. A.P. Mech. Deptt.

GUIDE PROJECT CO- ORDINATOR

The B.Tech viva voice Examination of Rishabh (2812493), Rajkishor (2812485), Ravi pandey (2812489), Shahzaib (2812484), Rishi (2812494), Ravi (2812235) has been held on future train (electricity generated from heat loss) and accepted.

(Er. SUNIL DHULL)

H.O.D. Signature of External Examiner

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ABSTRACT

Economic liberalization is finding good roots and globalization of economy is becoming a worldwide phenomenon, thus the present scenario calls for the optimum utilization for the best possible resources. With the growing environmental concerns and need of clean energy resources which don’t put nature at risk ( i.e., eco-friendly). In such a scenario our Future train with thermocouple module (Peltier chip) can be very advantageous for both humans and nature. From this we can generate electricity from heat loss and natural air. It is technique of future and can be very useful when coupled with technologies. Once established this technology will likely become common place due to increasing energy and environmental concerns and the ease of integration. Such Future Train will help our country to develop and prosper by less investment and more output of electricity as it is also clean and cheap from other technologies.

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ACKNOWLEDGEMENT

Words are inadequate and out of place at time particularly in the context of expressing sincere feeling in the contribution of this work, is no more than a mere ritual. It is our privilege to acknowledge with respect and gratitude, the keen valuable and ever-available guidance rendered to us by Er. Ajay singh ( Project Guide) without the wise counsel and able guidance, it would have been impossible to complete the project in this manner.

We shall always be highly grateful to Dr. K.K PALIWAL, Director, Panipat Institute of Engineering & Technology, samalkha, for providing this opportunity to carry out the present work. The constant guidance and encouragement received from Er. SUNIL DHULL, Asstt. Prof. & Head, Department of mechanical Engineering has been of great help field carrying out the present work and is acknowledged with reverential thanks.

We express gratitude to other faculty members of Mechanical Engineering Department, PIET, Samalkha for this intellectual support throughout the course of this work.

Finally, we are indebted to our family and for their ever available help in accomplishing this task successfully. Above all we are thankful to the Almighty God for giving strength to carry out the present work.

RISHABH (2812493)



SHAHZAIB (2812484)



Mechanical Engg. 7th sem

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CONTENTS

Page no.

Declaration 2

Abstract 3

Acknowledgement 4

List of figures 6

CHAPTER - 1Introduction 7

Research & Development 11

CHAPTER-2Components used 26

Summary 27

CHAPTER-3Invention of peltier chip 29

Uses 38

Results 39

Scope of future 40

References 42

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LIST OF FIGURES

FIGURE No. DESCRIPTION PAGE No.

1.1 Power generation from heat loss 8

1.2 How our train looks like 9

1.3 Harvesting energy 9

1.4 Thermal electric module 10

1.5 Emergency break 11

1.6 Deustsche shell 12

1.7 Industrial Reuse 13

1.8 Discarded heat 14

1.9 Fourth coming markets 13

1.10 Thermoelectric device 15

1.11 Thermoelectric material and application 16

1.12-1.13 Comparison 17

1.14 Mg2Si Cycle 18

1.15 Performance of Mg2Si 19

1.16 Si wafer fabrication system 20

1.17 Solar cell fabrication system 21

1.18 Reuse process 22

1.19 Conversion of waste silicon 23

1.20-1.21 Development status 23, 24

1.22 Mg2Si elements and module 25

1.23 Solar Thermal Power Generation 26

2.1-2.9 Components used 27

3.1 Charge carrier diffusion 34

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3.2 Three peltier module 36

3.3-3.4 Inside of module 36, 37

3.5 Electric current produce 38

3.6 Generation of electricity 38

3.7 Home power Station 40

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CHAPTER-1

INTRODUCTION

AIM OF PROJECT:

To harvest free energy for train bogies by exhaust heat energy loses from train engine.

PRINCIPLE USED IN PROJECT:

Our project is based on thermo coupling temperature difference principle.

We divided our project in two sections:

1. Power generation from heat losses2. Emergency brake applied in case of fire.

SECTION-1

POWER GENERATION FROM HEAT LOSSES

Fig-1.1 (Power generation from heat loss)

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HOW OUR TRAIN ENGINE LOOKS LIKE

Fig-1.2 (Train engine looks)

We will apply the thermocouple peltier setup on the train engine from there we can use the loss heat in the atmosphere and generate electricity by the temperature difference produced due to cool natural wind and engine heat.

HARVESTING ENERGY USE FOR LIGHT, COOLING (FAN ONLY) AND MOBILE, LAPTOP CHARGING

Fig1.3 (Harvesting energy)

Generating electricity from waste heat and free natural wind and using for human needs like mobile charging, laptop charging, lights, fans etc. This setup will decrease the cost.

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THERMOELECTRIC MODULE PLACEMENT

Fig1.4 (Thermoelectric moudle)

Thermoelectric module is placed between the engine and the fins so that the temperature difference can be created easily and we can genetrate electricity. We can also put nitogen gas into fins as nitrogen is a cool gas and more temperature difference will be created and hence more electricity is produced.

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SECTION-2

EMERGENCY BRAKE APPLIED IN CASE OF FIRE

Fig1.5 (Emergency brake)

We also added a extra feature in our future train model that is emergency brake system. In this we put a thermister it’s a heat sensing device , whenever there is fire produced in the coaches of train it will sense the heat and stop the train there only by applying emergency brakes.

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RESEARCH AND DEVELOPMENT

Development of the direct thermal-to-electric Power generator using environmentally, semiconducting material Solid-state power generation from waste heat and solar heat

Fig1.6 (Primary energy source)

This figure shows the range of primary energy sources that are anticipated in the near future (except for water power generation) as predicted by Deutsche Shell. In order to reduce CO2 emissions to counteract greenhouse effects, the accelerated introduction of renewable energies such as a solar cells and fuel cells based on pure hydrogen sources, seems to be very important to replace the use of fossil fuels. We believe that atomic power generation is not an eternal solution because of radioactive waste and resource abundance. On the other hand, since we cannot abandon the use of fossil fuels immediately, a positive attitude towards the use of waste heat is urgently required to sustain the huge growth in energy consumption on a world scale.

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Fig1.7 (Reuse )

We now believe that the industrial reuse of “Waste Heat” and “Waste Si” is definitely required for a sustainable society.

In the case of “Waste Heat” from caloric systems, this brings about an increase in CO2 emissions, and consequently to rises in atmospheric temperatures, which is becoming serious.

On the other hand, for “Waste Si” from the semiconductor industry, there are problems related to increases in Si waste, and, simultaneously, a lack of Si resources, as we are now beginning to recognize.

With increases in the production of LSI devices and solar cells, we will generate significant amounts of “Wandering Si waste” due to a lack of landfill capacity and associated environmental contamination by Si waste. This is also becoming a serious issue.

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Fig1.8 (Greenhouse effect)

The value of 11294.9 Mtoe (million tonnes oil equivalent : Mtoe) represents the total amount of primary energy consumption of the world last year.(BP statistical review of world energy 2009) Of this huge primary energy consumption, please consider that about 70 % of the installed primary energy is discarded as heat, resulting in increases in CO2 emissions and atmospheric temperature rises.By using a direct thermal-to-electric energy conversion technique, we would like to reuse this discarded heat energy in order to reduce CO2 emissions as soon as possible.

Fig1.9 (Fourthcoming market)

A major portion of this huge global primary energy consumption is consumed by two dominant countries, the United States and China, who consume about 20 % and 18 %, respectively. In these two countries, about 90 % of the primary energy is supplied by fossil fuels. From this point of view, these two countries will become the main target markets for new thermoelectric power plants

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Fig1.10 (Thermoelectric device)

This figure is a schematic illustration of the thermal-to-electric energy conversion; the so-called thermoelectric device.

One side of the thermoelectric device is heated by waste heat from such as industrial furnaces and automobile engines. The temperature difference between the hot-side and the cool -side can be used to generate electrical power. This is the mechanism for thermoelectric power generation.

As you can understand, the device structure is very simple and there are no moving parts, as compared with other competitive power generators such as gas turbines and the Stirling engine. These are remarkable advantages for thermoelectric power generation.

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Fig1.11 (Thermoelectric material and application)

This viewgraph shows various thermoelectric materials and their applications. Formerly, thermoelectric power generation was performed using Pb-Te, but, as you know, these days regulations such as ROHS and REACH in the EU prohibit the development of Pb-Te thermoelectric devices.

As alternative materials, Co-Sb, Zn-Sb and TAGS have been developed, but I should point out that these materials still contain harmful substances, so they are not really solutions in terms of ROHS and REACH regulations.

From this point of view, we have been trying to fabricate environmentally benign thermoelectric materials from Mg2Si. The constituent elements of Mg and Si are abundant and are non-toxic. Additionally, Mg2Si itself and its by-products are not included in the scope of regulations covering harmful substances.

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Fig1.12 (conversion)

Fig1.13 (Conversion)

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Fig1.14(Cycle of magnesium silicate)

The above tables show comparisons of the conversion efficiency, abundance, material cost, and toxicity for Mg2Si and other related materials. The expected value for the conversion efficiency of Mg2Si is 9.5 % for each “element” (Japanese NEDO target value), where an “element” consists of a device structure equipped with an electrode, a thermal contact and associated electronics. Compared with other materials, Mg2Si exhibits comparable or slightly higher energy conversion efficiency. Since Mg2Si is a very light material, if we refer to the value of efficiency divided by material density, the index that we obtain exhibits much higher values.

In a comparison of relative abundance, material cost, and the need for environmentally hazardous substances, Mg2Si is exemplary. Its constituent elements Si and Mg are readily available, it has sufficient energy conversion efficiency, and its non-toxic nature means it can be discarded safely after its lifetime.

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Fig1.15 (Performance of mg2si)

This figure shows the measured performance of fabricated Mg2Si devices at elevated operating temperatures.

Typically, we consult the value of the figure of merit, ZT, to quantify the available material conversion efficiency. ZT = 1 stands for about 10% material conversion efficiency.

In the case of Mg2Si, we have already obtained a ZT value of 1.1, indicating greater than 11 % material conversion efficiency. We can therefore say that environmentally benign Mg2Si is a very promising material on which to base a system for reusing waste heat.

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Fig1.16 (Wafer fabrication process)

This is a schematic illustration of the silicon (Si) wafer fabrication process.In general, Si wafer fabrication begins with polycrystalline Si and nuggets.

After the crystal growth process by means of the Czochralski (CZ) method, we end up with a single-crystal Si ingot. In order to obtain a Si wafer that can be used for electronic device fabrication such as LSI, the grown Si ingot is sliced using a sawing machine, and then mirror-like polishing is carried out.

During these wafer-fabrication processes, about 60 % of the initial Si source is discarded as Si sludge. Since the production of 1 kg of Si wafers requires ~1000 kWh electricity, a large amount of energy is used to produce discarded Si sludge. This is an awful state of affairs.

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Fig1.17 (Solar cell fabrication system)

This is a schematic illustration of the LSI-fabrication and the cast solar-cell fabrication processes.Back-grinding of LSI embedded wafers and sawing of cast Si ingots also produce Si sludge.

During the device fabrication process, ~60 to 70 % of the Si from the initial ingot is discarded. As we are recognizing, the increase in discarded Si from wafers and from device fabrication processes is becoming serious in terms of the lack of land fill capacity and environmental contamination.

Last year we experienced a serious lack of semiconductor-grade and solar-cell-grade Si source material, while huge amounts of Si sludge were emitted as industrial waste in concurrence. This seems to be an inconsistent situation. I would like to attain a “reuse-Si cycle” using waste Si as a new angle on the Si problem in the semiconductor industry.

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Fig1.18 (Reuse process)

One interesting approach of our Mg2Si development is the introduction of waste Si as a starting source material. The waste Si sludge is provided from an LSI fab producing CPUs, memories, power IC devices, and baseband chips for mobile phones.

In addition, solar cell factories also emit Si waste which is of utility value for Mg2Si synthesis. Recently, we have developed a low-cost purification process for the waste Si sludge, in order to improve the fabrication process for Mg2Si.

The thermal-to-electric conversion performance of Mg2Si devices fabricated using purified ‘reuse-Si’ and less pure Mg sources exhibits practically the same power generation ability compared with other Mg2Si devices synthesized from pure Si and Mg sources.

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Fig1.19 (Conversion of wested silicon)

By means of “Waste Si”, we would like to produce a “Waste Heat” reuse system based on the environmentally begin semiconductor material Mg2Si. We believe that this approach could serve as an aid for the restrain to the greenhouse effect and the global energy crisis. “The future must be wonderful”. Such a strong statement is a source of motivation toward making these improvements.

Fig1.20 (Development status)

For the past few decades, Mg2Si has been recognized as a good TE material, but it also has been identified as very difficult to synthesize with good crystalline quality. This is mainly due to the dangerous process temperature required for the melt growth of Mg2Si.

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The melting point of Mg2Si is 1085°C, and thus ~1150°C or slightly higher temperature is needed for obtain good crystalline quality.

However, this desirable process temperature is beyond the “boiling temperature (1090°C)” of Mg. This is why Mg2Si has not been pursued extensively, even though Mg2Si is anticipated as a candidate for thermo electric material. We provocatively inaugurated a plan to develop a possible growth method for Mg2Si back in the year 2000.

Fig1.21 (Development status)

In 2000, as our first action, we tried to fabricate single crystal Mg2Si, and we successfully developed a synthesis technique for this material. For the grown Mg2Si, the measured thermoelectric performance and durability at elevated temperature were sufficient for practical use. In 2003, we then tried to reduce the fabrication cost to establish commercial Mg2Si material using refined synthesis methods.

Starting from 2005, we examined the introduction of Si sludge and recycled Mg-alloy as source materials for Mg2Si fabrication by developing a low-cost purification process. We have now achieved a “Mg2Si for waste heat reuse device” using waste Si and recycled Mg sources. So far, our approach to making Mg2Si has been epochal. From 2009, we have started to fabricate Mg2Si thermoelectric power generation modules, and have executed field tests of the modules at various industrial moderate-temperature heat sources.

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Fig1.22 (Element and module)

The fabricated Mg2Si thermoelectric elements and modules are shown here. Since the measured power generation ability of Mg2Si is large enough, we have just started the development of specific modules for solar heat power generation.

The typical current power generation density of this material is about 2.5 to 3 kW/m2, and tentative life tests (hot side: 600 °C, cool side: 100 °C, in the air) have lasted for more than 15,000 hrs with neither remarkable power drop nor surface degradation.

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Fig1.23 (Solar thermal power generation)

Since the current power density of these Mg2Si thermoelectric elements is large enough, we have been able to examine the development a specific Mg2Si modules for solar thermal power generation.

An SES solar thermal power generator using a Stirling engine already exists in California, as shown in the picture below.

This type of power generator is also available for Mg2Si solid-state thermoelectric power-generation by replacing the Stirling engine with a thermoelectric device.

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CHAPTER-2

COMPONENTS USED

1. Thermocouple module ( 6V/7V)

Fig 2.12. Transformer (12012,1Amp)

Fig 2.2

3. Relay (12V)

Fig 2.34. Blower (24V DC)

Fig 2.4

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5. Motor (12V DC)

Fig 2.5

6. Heating press element (220V AC)

Fig 2.67. Digital multimeter

Fig 2.78. Thermester

Fig 2.8

9. Bridge wave Rectifier (4 diode-1N4007 PN junction)

Fig 2.9

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CHAPTER-3

Invention of peltire chip

Jean Charles Athanase Peltier (1785 in Ham (France) - 1845 in Paris) was a French physicist. He discovered the calorific effect of electric current passing through the junction of two different metals. This is now called the Peltier effect or Peltier–Seebeck effect.

The Peltier effect, where current is forced through a junction of two different metals, forms the basis of the small 12/24 Volt heater/coolers sold for vehicle use. By switching the direction of current, either heating or cooling may be achieved. It also forms the basis of the rather expensive, but very stable, junction heated soldering irons, and is used for spot cooling of certain integrated circuits.

It is important to realise that junctions always come in pairs, as the two different metals must be joined at two points. Thus heat will be moved from one junction to the other. To make a usable heat pump, multiple junctions are created between two plates. One side will get hot and the other side cold. An effective heat dissipation device must be attached to the hot side to maintain a cooling effect on the cold side. This is usually a heat sink and fan assembly.

Thermoelectric effect

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect). At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally-induced current.

This effect can be used to generate electricity, to measure temperature, to cool objects, or to heat them or cook them. Because the direction of heating and cooling is determined by the sign of the applied voltage, thermoelectric devices make very convenient temperature controllers.

Traditionally, the term thermoelectric effect or thermoelectricity encompasses three separately identified effects, the Seebeck effect, the Peltier effect, and the Thomson effect. In many textbooks, thermoelectric effect may also be called the Peltier–Seebeck effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and Estonian-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is somewhat related, though it is not generally termed a thermoelectric effect (and it is usually regarded as being a loss mechanism due to non-ideality in thermoelectric devices). The Peltier–Seebeck and Thomson effects can in principle be thermodynamically reversible, whereas Joule heating is not.

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Seebeck effect

The Seebeck effect is the conversion of temperature differences directly into electricity.

Seebeck discovered that a compass needle would be deflected when a closed loop was formed of two metals joined in two places with a temperature difference between the junctions. This is because the metals respond differently to the temperature difference, which creates a current loop, which produces a magnetic field. Seebeck, however, at this time did not recognize there was an electric current involved, so he called the phenomenon the thermomagnetic effect, thinking that the two metals became magnetically polarized by the temperature gradient. The Danish physicist Hans Christian Ørsted played a vital role in explaining and conceiving the term "thermoelectricity".

The effect is that a voltage, the thermoelectric EMF, is created in the presence of a temperature difference between two different metals or semiconductors. This causes a continuous current in the conductors if they form a complete loop. The voltage created is of the order of several microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck coefficient of 41 microvolts per kelvin at room temperature.

In the circuit:

(which can be in several different configurations and be governed by the same equations) , the voltage developed can be derived from:

SA and SB are the Seebeck coefficients (also called thermoelectric power or thermo power) of the metals A and B as a function of temperature, and T1 and T2 are the temperatures of the two junctions. The Seebeck coefficients are non-linear as a function of temperature, and depend on the conductors' absolute temperature, material, and molecular structure. If the Seebeck coefficients are effectively constant for the measured temperature range, the above formula can be approximated as:

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The Seebeck effect is commonly used in a device called a thermocouple (because it is made from a coupling or junction of materials, usually metals) to measure a temperature difference directly or to measure an absolute temperature by setting one end to a known temperature. A metal of unknown composition can be classified by its TE effect if a metallic probe of known composition, kept at a constant temperature, is held in contact with it. Industrial quality control instruments use this Seebeck effect to identify metal alloys. This is known as Thermo electric alloy sorting. Several thermocouples when connected in series are called a thermopile, which is sometimes constructed in order to increase the output voltage since the voltage induced over each individual couple is small.

This is also the principle at work behind thermal diodes and thermoelectric generators (such as radioisotope thermoelectric generators or RTGs) which are used for creating power from heat differentials.

The Seebeck effect is due to two effects: charge carrier diffusion and phonon drag (described below). If both connections are held at the same temperature, but one connection is periodically opened and closed, an AC voltage is measured, which is also temperature dependent. This application of the Kelvin probe is sometimes used to argue that the underlying physics only needs one junction. And this effect is still visible if the wires only come close, but do not touch, thus no diffusion is needed.

Thermo power

The thermo power, thermoelectric power, or Seebeck coefficient of a material measures the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material. The thermo power has units of (V/K), though in practice it is more common to use microvolts per kelvin. Values in the hundreds of μV/K, negative or positive, are typical of good thermoelectric materials. The term thermo power is a misnomer since it measures the voltage or electric field induced in response to a temperature difference, not the electric power. An applied temperature difference causes charged carriers in the material, whether they are electrons or holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated. Mobile charged carriers migrating to the cold side leave behind their oppositely charged and immobile nuclei at the hot side thus giving rise to a thermoelectric voltage (thermoelectric refers to the fact that the voltage is created by a temperature difference). Since a separation of charges also creates an electric potential, the buildup of charged carriers onto the cold side eventually ceases at some maximum value since there exists an equal amount of charged carriers drifting back to the hot side as a result of the electric field at equilibrium. Only an increase in the temperature difference can resume a buildup of more charge carriers on the cold side and thus lead to an increase in the thermoelectric voltage. Incidentally the thermo power also measures the entropy per charge carrier in the material. To be more specific, the partial molar electronic

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heat capacity is said to equal the absolute thermoelectric power multiplied by the negative of Faraday's constant.

The thermo power of a material, represented by S (or sometimes by α), depends on the material's temperature and crystal structure. Typically metals have small thermo powers because most have half-filled bands. Electrons (negative charges) and holes (positive charges) both contribute to the induced thermoelectric voltage thus canceling each other's contribution to that voltage and making it small. In contrast, semiconductors can be doped with excess electrons or holes, and thus can have large positive or negative values of the thermo power depending on the charge of the excess carriers. The sign of the thermo power can determine which charged carriers dominate the electric transport in both metals and semiconductors.

If the temperature difference ΔT between the two ends of a material is small, then the thermo power of a material is defined (approximately) as:

and a thermoelectric voltage ΔV is seen at the terminals.

This can also be written in relation to the electric field E and the temperature gradient , by the approximate equation.

In practice one rarely measures the absolute thermo power of the material of interest. This is because electrodes attached to a voltmeter must be placed onto the material in order to measure the thermoelectric voltage. The temperature gradient then also typically induces a thermoelectric voltage across one leg of the measurement electrodes. Therefore the measured thermo power includes a contribution from the thermo power of the material of interest and the material of the measurement electrodes.

The measured thermo power is then a contribution from both and can be written as:

Superconductors have zero thermo power since the charged carriers produce no entropy. This allows a direct measurement of the absolute thermo power of the material of interest, since it is the thermo power of the entire thermocouple as well. In addition, a measurement of the Thomson coefficient, μ, of a material can also yield the thermo power through the relation:

The thermo power is an important material parameter that determines the efficiency of a thermoelectric material. A larger induced thermoelectric voltage for a given temperature gradient will lead to a larger efficiency. Ideally one would want very large thermo power values since only a small amount of heat is then necessary to create a large voltage. This voltage can then be used to provide power.

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Charge-carrier diffusion

Charge carriers in the materials (electrons in metals, electrons and holes in semiconductors, ions in ionic conductors) will diffuse when one end of a conductor is at a different temperature than the other. Hot carriers diffuse from the hot end to the cold end, since there is a lower density of hot carriers at the cold end of the conductor. Cold carriers diffuse from the cold end to the hot end for the same reason.

If the conductor were left to reach thermodynamic equilibrium, this process would result in heat being distributed evenly throughout the conductor The movement of heat (in the form of hot charge carriers) from one end to the other is called a heat current. As charge carriers are moving, it is also an electrical current.

In a system where both ends are kept at a constant temperature difference (a constant heat current from one end to the other), there is a constant diffusion of carriers. If the rate of diffusion of hot and cold carriers in opposite directions were equal, there would be no net change in charge. However, the diffusing charges are scattered by impurities, imperfections, and lattice vibrations (phonons). If the scattering is energy dependent, the hot and cold carriers will diffuse at different rates. This creates a higher density of carriers at one end of the material, and the distance between the positive and negative charges produces a potential difference; an electrostatic voltage.

This electric field, however, opposes the uneven scattering of carriers, and an equilibrium is reached where the net number of carriers diffusing in one direction is canceled by the net number of carriers moving in the opposite direction from the electrostatic field. This means the thermo power of a material depends greatly on impurities, imperfections, and structural changes (which often vary themselves with temperature and electric field), and the thermo power of a material is a collection of many different effects.

Early thermocouples were metallic, but many more recently developed thermoelectric devices are made from alternating p-type and n-type semiconductor elements connected by metallic interconnects as pictured in the figures below. Semiconductor junctions are especially common in power generation devices, while metallic junctions are more common in temperature measurement. Charge flows through the n-type element, crosses a metallic interconnect, and passes into the p-type element. If a power source is provided, the thermoelectric device may act as a cooler, as in the figure to the left below. This is the Peltier effect, described below.

Electrons in the n-type element will move opposite the direction of current and holes in the p-type element will move in the direction of current, both removing heat from one side of the device. If a heat source is provided, the thermoelectric device may function as a power generator, as in the figure to the right below. The heat source will drive electrons in the n-type element toward the cooler region, thus creating a current through the circuit.

Holes in the p-type element will then flow in the direction of the current. The current can then be used to power a load, thus converting the thermal energy into electrical energy.

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Fig3.1 (Charge carrier diffusion)

Phonon drag

Phonons are not always in local thermal equilibrium; they move against the thermal gradient. They lose momentum by interacting with electrons (or other carriers) and imperfections in the crystal. If the phonon-electron interaction is predominant, the phonons will tend to push the electrons to one end of the material, losing momentum in the process. This contributes to the already present thermoelectric field.

This contribution is most important in the temperature region where phonon-electron scattering is predominant. This happens for

Where θD is the Debye temperature. At lower temperatures there are fewer phonons available for drag, and at higher temperatures they tend to lose momentum in phonon-phonon scattering instead of phonon-electron scattering.

This region of the thermo power-versus-temperature function is highly variable under a magnetic field.

Peltier effect

The Peltier (pronounced /ˈpɛltyeɪ/) effect bears the name of Jean-Charles Peltier, a French physicist who in 1834 discovered the calorific effect of an electrical current at the junction of two different metals. When a current I is made to flow through the circuit, heat is evolved at the upper junction (at T2), and absorbed at the lower junction (at T1). The Peltier heat absorbed by the lower junction per unit time, Q is equal to .

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Where Π is the Peltier coefficient ΠAB of the entire thermocouple, and ΠA and ΠB are the coefficients of each material. p-type silicon typically has a positive Peltier coefficient (though not above ~550 K), and n-type silicon is typically negative.

The Peltier coefficients represent how much heat current is carried per unit charge through a given material. Since charge current must be continuous across a junction, the associated heat flow will develop a discontinuity if ΠA and ΠB are different.

This causes a non-zero divergence at the junction and so heat must accumulate or deplete there, depending on the sign of the current. Another way to understand how this effect could cool a junction is to note that when electrons flow from a region of high density to a region of low density, they expand (as with an ideal gas) and cool.

The conductors are attempting to return to the electron equilibrium that existed before the current was applied by absorbing energy at one connector and releasing it at the other. The individual couples can be connected in series to enhance the effect.

An interesting consequence of this effect is that the direction of heat transfer is controlled by the polarity of the current; reversing the polarity will change the direction of transfer and thus the sign of the heat absorbed/evolved

.A Peltier cooler/heater or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other. Peltier cooling is also called thermo-electric cooling (TEC).

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Three Peltier Modules:

Fig3.2 (Peltier module)

Inside of a couple module:

Fig3.3 (Incide view of peltire module)

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Close-up of inside of a module:

Note: metallized connecting bars on ceramic plate on the left. These serve to connect all of the couples in series.

Fig3.4 (View of module)

HOW IT WORKS:

TEGs are made from thermoelectric modules which are solid-state integrated circuits that employ three established thermoelectric effects known as the Peltier, Seebeck and Thomson effects. It is the Seebeck effect that is responsible for electrical power generation.

Their construction consists of pairs of p-type and n-type semiconductor materials forming a thermocouple. These thermocouples are then connected electrically forming an array of multiple thermocouples (thermopile). They are then sandwiched between two thin ceramic wafers.

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When heat and cold are applied, the device then generates electricity.

Fig3.5 (Process to generate electricity)

These thermocouples are then connected electrically in series and/or parallel forming an array of multiple thermocouples (thermopile). When heat and cold are applied this device then generates electricity. Almost any heat source can be used to generate electricity, such as solar heat, ocean heat, geothermal heat, even body heat! In addition the efficiency of any device or machine that generates heat as a by-product can be drastically improved by recovering the energy lost as heat.

Can you really generate that much electricity from waste heat?

You may be surprised just how much you can! Here is a small example of how much power you can generate. Below is a pot of hot water with 4-thermoelectric modules attached around the sides. The output from this simple thermoelectric generator (TEG) is about 8 watt and the light is a 12 volt auto lamp.

Fig 3.6 (Generation of electriciy)

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Thermoelectric generators have been in use for many years by NASA to power spacecraft and the oil and gas industry to power remote monitoring stations around the globe.

Only in recent years has this technology become available to the general public and TEG Power is at the forefront of this thermoelectric energy revolution. We are the first manufacture to provide practical and affordable thermoelectric generators to the energy conscious consumer.

Almost any heat source can be used to generate electricity, such as solar heat, ocean heat, geothermal heat, even body heat!

NOTE:

One 165 watt Sharp PV panel produces 0.6 kWh of electricity per day in sunny Southern California. One 25 watt TEG also produces 0.6 kWh of electricity per day (with a continuous heat source) day or night.

When you compare the costs of solar and our thermoelectric generators based on the amount of electricity they actually produce per day, you find that our TEGs cost far less per kWh than solar! The PV (photovoltaic) equivalent of 50 watts of TEG power operating on a wood stove is 330 watts of solar panels or 1.2 kWh per day. This means using just 150 watts thermoelectric power can produce the same amount of electricity in a day as 990 watts of solar PV panels.

If comparing costs, the price range for 990 watts of solar would be as much as $5,000 depending on the particular brand. Whereas the cost of 150 watts of thermoelectric power can be as low as $500. Unlike solar TEGs are not dependant on the sun to producing electric power. If you have a continuous heat source, like a wood stove, TEGs can produce power day and night, 24/7-365. Granted you will need a cheap or free source of heat, but if you already have an existing heat source such as a wood stove or hot flu gases there is no added fuel cost to run the TEG! Unlike conventional electric generators powered by fossil fuels, TEGs have no moving parts to break. They are virtually silent and rated to last more than 200,000 hours of continuous operation.

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Home Power Stations:

One possible use for thermoelectric generators is to provide supplemental or back-up electricity for home owners who use outdoor wood/biofuel furnaces. The diagram below reflects just one of the possible thermoelectric home power stations that could be setup using TEGs. It should be noted that just 500 watts of thermoelectric power added to an outdoor wood/biofuel furnace like the one below can produce 12 kWh of electricity per day, which is enough to reduce the average household electric bill by more than one third, based on an average household usage of 30.66 kWh per day. The vast majority of wood burning furnaces today use gasification technology which produces clean burning hydrogen gas, making them extremely efficient and clean burning.

Fig3.7 (Home power station)

The need for thermoelectric power . .

Electricity is no longer a luxury; it has become a necessity in our everyday lives. Have you ever had to live without electricity for an extended period of time? If so then you know what it is like to lose all the food in your refrigerator and/or chest freezer and shivering in the cold because you have no heat.

Every year thousands, even millions have been in this position when a winter storm knocked out power over large areas. Not to mention rapidly rising energy costs and an uncertain economic future. Still many people have become complacent about their electrical energy needs. Solar panels are a great alternative energy source, but they only produce electricity during daylight hours.In addition their daily output is significantly reduced during winter months and cloudy days. Now, using a TEG in conjunction with solar and wind, their combined output can provide

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all off your home’s energy needs and depending on what state you live in, you will be getting a check from the electric company instead off a bill.

Results

Electricity has been generated by applying Peltier chip on the engine of the train when the train is in motion i.e, when natural air is striking at one side of the peltier chip and hence due to temp. difference we can generate electricity out of waste heat. It can be used for mobile charging, laptop charging, fan and tube lights. Here in the model we used heating press element instead of engine and blower instead of natural air and we are able to produce electricity upto 3V with the help of generated electricity we are using a small fan.

We also used thermesters (heat sensing device) for emergency braking system in train during the case of accidental fire. It will stop the moving train whenever it senses heat and emergency brakes will be applied.

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Scope for future

Since it is a eco-friendly technology hence will be appreciated in all areas. The peltier chip consist of magnesium silicate which is not costly, easily available and does not have toxicity. With this greenhouse effect will be controlled no depletion of ozone layer. No pollution will get into the atmosphere and can be used to generate electricity where a good temp. Difference is present. This technology is very useful and can be used to generate electricity efficiently in a clean manner. With the decrease in fuel percentage there is a utmost importance of this technology to be used in many sectors for electricity generation.

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References

1. http://www.physorg.com/news142847923.html2. Rowe, D. M., ed (2006). Thermoelectric Handbook3. Thomson, William (1851). "On a mechanical theory of thermoelectric currents".4. Katie Walter (May 2007). "A Quantum contribution to Technology

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